Beam filter positioning device

ABSTRACT

A system includes a beam filter positioning device including a plate configured to support one or more beam filters, and one or more axes operable to move the plate relative to a beam line. A control mechanism is coupled to the one or more axes for controlling the movement of the axes and configured to automatically adjust the position of at least one of the one or more beam filters relative to the beam line.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/568,619 filed Sep. 28, 2009, now U.S. Pat. No. 8,077,830, thedisclosure of which is incorporated herein by reference.

BACKGROUND

This invention relates generally to X-ray apparatuses and in particularto beam filter positioning devices and linear accelerators incorporatingthe same.

Linear accelerators are used in a variety of industries including inmedical radiation therapy and imaging. A linear accelerator includes atreatment head that houses various components configured to produce,shape or monitor a treatment beam. For example, a target produces X-rayswhen it is impinged by energetic electrons. A photon flattening filtershapes X-rays to provide a uniform dose distribution across the X-rayfield. An ion chamber monitors the energy, dose distribution, dose rate,or other parameters of a radiation beam. In an electron mode operation,an electron scattering foil scatters incident electrons to provide abroadened, uniform profile of a treatment beam. A field light systemsimulates a treatment field by illuminating e.g. an area on the surfaceof a patient's skin.

In conventional accelerators, exchangers are used to position electronscattering foils and photon flattening filters. Foil-filter exchangersallow switching back and forth between scattering foils and flatteningfilters for electron or photon mode operations. Fine precisionadjustments of the foils and filters in exchangers are accomplished inthe factory by manually adjusting and testing the foils and filters,which is a very time consuming process.

Conventional foil-filter exchangers do not include a target assembly orfield light assembly. In conventional accelerators the targets arelocated in other areas of the treatment head e.g. inside the acceleratorvacuum envelope. The design of target assemblies residing inside thevacuum envelop is complex due to added vacuum walls and interfaceconsiderations. Actuation of targets in vacuum is complicated. Any waterleaks in target cooling systems would contaminate the vacuum envelopecausing extended downtime.

A field light system includes a lamp and a mirror, and is used tofacilitate patient placement for treatment by providing an intense lightfield that coincides with the radiation treatment field shaped bycollimator jaws or other beam limiting devices. Because of spacelimitations and other considerations, it is unfeasible to place a lampin the same location as the radiation source. In conventionalaccelerators the mirror is fixedly disposed along the beam centerlineand is made of a thin film that is generally transparent to radiation orelectron beams. Once being installed, the mirror and the lamp projectorare manually adjusted in order to achieve the required coincidence withthe X-ray field. The mirror located in the beam centerline causesscattering losses and beam contamination. The thin film materials aresusceptible to degradation due to exposure to radiation, damage andoptical distortion.

SUMMARY

The present invention provides a beam filter positioning device thatallows for significant improvement in automation of production testprocedures and operation of medical linear accelerators. It providessignificant savings in both test time and occupancy of final test. Thebeam filter positioning device performs multiple functions in producing,shaping, or monitoring a treatment beam. For instance, the device mayposition a target button under an electron beam to produce X-rays in aphoton mode, or retract a target out of the path of an electron beam foran electron or other modes. The device may accurately position anelectron scattering foil or a photon flattening filter to shape theintensity profile of a treatment beam and provide uniform treatmentfields. The device may precisely position a field light assembly insimulating a treatment beam for patient alignment. It may also retractan ion chamber from the beam centerline to provide an unimpeded path forthe field light. The beam filter positioning device may be modular. Itcan be mounted to the treatment head of an accelerator and easilyremoved for repair with proper lifting fixtures. Driving mechanisms suchas servo motor control may be used to perform precise movement oradjustments of various device components.

In one embodiment, a carousel assembly includes a base plate, a stagesupported by the base plate and movable in a linear direction, afilter-foil assembly attached to the stage, a target assembly supportedby the base plate, and an ion chamber assembly supported by the baseplate. The filter-foil assembly is rotatable about an axis, movable in alinear direction with the stage, and includes a plate member adapted tosupport one or more photon flattening filters and one or more electronscattering foils. The target assembly includes one or more targets andis movable in a linear direction. The ion chamber assembly is movable ina linear direction.

In some embodiments, the carousel assembly may include a field lightassembly having a mirror member and a light source. The mirror member ispreferably supported by the filter-foil assembly, and the light sourceis supported by the ion chamber assembly. In a preferred embodiment, thelight source includes two or more lamps each being operable to projectlight to the mirror member for the purposes of providing redundancy.

In some embodiments, the carousel assembly may additionally include abackscatter filter assembly attached to the filter-foil assembly.

In a preferred embodiment, a plurality of photon flattening filters arepositioned in a circular or partial circular configuration having afirst radius, and a plurality of electron scattering foils arepositioned in a circular or partial circular configuration having asecond radius different from the first radius. The second radius ispreferably greater than the first radius.

In one embodiment, a carousel assembly includes a plate adapted tosupport one or more photon flattening filters and one or more electronscattering foils, a first linear axis operable to move the plate in alinear direction, and a rotation axis operable to rotate the plate aboutan axis. In a preferred embodiment, the first linear axis is operable tomove the rotation axis in a linear direction. Preferably, the firstlinear axis and/or the rotation axis comprise a servo motor controllableby a computer.

In some embodiments, a plurality of photon flattening filters arepositioned in a circular or partial circular configuration having afirst radius, and plurality of electron scattering foils are positionedin a circular or partial circular configuration having a second radiusdifferent from the first radius. The second radius is preferably greaterthan the first radius.

In one aspect, a system comprises a beam filter positioning device and acontrol mechanism. The beam filter positioning device comprises a plateconfigured to support one or more beam filters, and one or more axesoperable to move the plate relative to a beam line. The controlmechanism is coupled to the one or more axes for controlling themovement of the axes and configured to automatically adjust a positionof at least one of the beam filters relative to the beam line.

In another aspect, a beam filter positioning device comprises a plateconfigured to support one or more beam filters, and two or more axesoperable to move the plate. The two or more axes may comprise a linearaxis operable to translate the plate and a rotation axis operable torotate the plate. In a preferred embodiment, the linear axis is operableto translate the rotation axis.

In a further aspect, a method of automatically adjusting a beam filterposition in a radiation system comprises the steps of providing a plateand one or more beam filters supported by the plate, and moving theplate using one or more motion axes to position a beam filter relativeto a beam line. A control mechanism operable by computer software isused to automatically adjust the position of a beam filter in theradiation system.

In a further aspect, a method of automatically adjusting field light ina radiation system comprises the steps of providing a field lightassembly including a mirror and a light source, moving the mirror usinga first motion axis and/or moving the light source using a second motionaxis to provide a light field that would illuminate from a virtual lightsource. The moving of the mirror and/or the light source is controlledby a control mechanism operable by computer software, whereby thevirtual light source position is automatically adjustable in threedegrees of freedom.

BRIEF DESCRIPTION OF THE DRAWINGS

These and various other features and advantages will become betterunderstood upon reading of the following detailed description inconjunction with the accompanying drawings and the appended claimsprovided below, where:

FIG. 1A is a top perspective view of a beam filter positioning device inaccordance with some embodiments of the invention;

FIG. 1B is a bottom perspective view of a beam filter positioning devicein accordance with some embodiments of the invention;

FIG. 1C is a cut-way view of a beam filter positioning device inaccordance with some embodiments of the invention;

FIG. 1D is an exploded view of a beam filter positioning device inaccordance with some embodiments of the invention;

FIG. 2 is a bottom perspective view, with the beam filter assembly andthe ion chamber not shown for clarity, showing a movable stage and abase plate in accordance with some embodiments of the invention;

FIG. 3 is a perspective view of a beam filter assembly in accordancewith some embodiments of the invention;

FIG. 4 is a perspective view of an ion chamber assembly in accordancewith some embodiments of the invention;

FIG. 5 is a top perspective view of a target assembly in accordance withsome embodiments of the invention;

FIG. 6 is a cut-way view of a beam filter positioning device in a photonmode in accordance with some embodiments of the invention;

FIG. 7 is a cut-way view of a beam filter positioning device in anelectron mode in accordance with some embodiments of the invention; and

FIG. 8 is a cut-away view of a beam filter positioning device in a fieldlight simulation mode in accordance with some embodiments of theinvention.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

Various embodiments of beam filter positioning devices and linearaccelerators incorporating the devices are described. It is to beunderstood that the invention is not limited to the particularembodiments described as such may, of course, vary. An aspect describedin conjunction with a particular embodiment is not necessarily limitedto that embodiment and can be practiced in any other embodiments. Forinstance, while various embodiments are described in connection withX-ray linear accelerators, it will be appreciated that the invention canalso be practiced in other particle accelerators. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting since the scope of the invention will be limited only by theappended claims, along with the full scope of equivalents to which suchclaims are entitled. The term “carousel” is sometimes used to describean embodiment that uses a rotational axis; but the invention is notlimited to such an embodiment.

In addition, various embodiments are described with reference to thefigures. It should be noted that the figures are not drawn to scale, andare only intended to facilitate the description of specific embodiments.They are not intended as an exhaustive description or as a limitation onthe scope of the invention.

All technical and scientific terms used herein have the same meaning ascommonly understood by one of ordinary skill in the art to which thisinvention belongs, unless defined otherwise. Various relative terms usedin the description or appended claims such as “above,” “under,” “upper,”“over,” “on,” top,” “bottom,” “higher,” and “lower” etc. are definedwith respect to the conventional plane or surface being on the topsurface of the structure, regardless of the orientation of thestructure, and do not necessarily represent an orientation used duringmanufacture or use. The following detailed description is, therefore,not to be taken in a limiting sense. As used in the description andappended claims, the singular forms of “a,” “an,” and “the” includeplural references unless the context clearly dictates otherwise.

As used herein the term “beam filter” refers to a member that modulatesone or more parameters of a particle beam such as the energy, intensity,shape, direction, dose distribution, or other beam parameters. Aparticle beam includes but is not limited to a beam of electrons,photons, protons, heavy ions, or other particles. By way of example, abeam filter includes but is not limited to a photon flattening filter,an electron scattering foil, and a proton scattering foil.

As used herein, the term “axis” refers to a mechanism that is operableto move an object in a direction. For example, a “linear axis” refers toa mechanism that is operable to move an object in a linear direction. A“rotation axis” refers to a mechanism that is operable to rotate anobject around an axis. An axis may preferably include a servo motor andone or more feedback devices that are electrically coupled to a controlmechanism operable with user interface software. A close loop controlcan be used to control the axis and automatically adjust the position ofan object in a system.

FIGS. 1A-1D illustrate an exemplary carousel assembly or beam filterpositioning device 100 in accordance with some embodiments of theinvention. The device 100 may include a movable stage 200, a beam filterassembly or photon flattening filter-electron scattering foil assembly300 (hereafter “filter-foil assembly” for simplicity of description), anion chamber assembly 400, a field light assembly 450, and a targetassembly 500. The device 100 may also include a backscatter filter 460.The movable stage 200, filter-foil assembly 300, ion chamber assembly400, field light assembly 450, target assembly 500, and various drivingmechanisms or axes are preferably coupled to or supported by asupporting structure 202 such as a frame, a base plate, or the like.

FIG. 2 is a bottom perspective view, with the filter-foil assembly andion chamber not shown for clarity, showing a stage 200 and a base plate202. The base plate 202 is configured to be mounted to a treatment headand provides support for the device 100. A frame 204 is attached to thebase plate 202 along its periphery providing additional support andstiffness for the device 100. The base plate 202 has a cutout 206 e.g.in a generally rectangular shape defining an open area under which thestage 200 is located.

The stage 200 supports a primary collimator 208, shielding 210,shielding 224, and filter-foil assembly 300 etc. (see also FIG. 1A), andis operable to move its payload in a direction. For example, the stage200 can be driven by a linear axis 212 and moved along a direction suchas a direction parallel to a linear accelerator plane of symmetry(Y-direction) or other directions. Alternatively, the stage 200 can bedriven by a rotation axis and rotate in a direction. The linear axis 212may include a motor 212 a, a ball screw 212 b, and a coupler 212 ccoupling the motor and the ball screw. The motor 212 a and ball screw212 b can be supported by mounts 214, 216 respectively. The motor 212 aserves to rotate the ball screw 212 b, which is adapted to engage thestage 200 and move the stage 200 in a linear direction. Guide rails 218a, 218 b fixedly attached to the base plate 202 define the linearmovement of the stage 200. Slide guides or other mechanisms (not shown)can be used to engage the stage 200 with the guide rails 218 a, 218 b. Aresolver or sensor 212 d may be coupled to the motor 212 a to provideprimary feedback on the position of the ball screw. A housed resolver212 e may be used to provide redundant or secondary feedback.Preferably, the motor 212 a is a servo motor electrically connected to acontroller and operable with user interface software. While a specificmotor, ball screw, guide, and feedbacks are described in detail forillustrative purposes, it should be appreciated that other types ofdrive mechanisms or feedbacks can also be used and anticipated by theinventors.

The stage 200 may have an opening adapted to receive the primarycollimator 208 (see also FIG. 1C). The primary collimator 208 may beprovided with a step on the bottom side so that it can fit in theopening and held in place. Pins, screws, and other suitable means can beused to secure the primary collimator 208 to the stage 200. The primarycollimator 208 can be made of tungsten or other suitable high densitymetals. The primary collimator 208 is provided with a passageway 222(see also FIG. 1C) e.g. in a cone shape to define or shape the field ofX-rays produced. Shielding 224 is located under the stage 200 and can beattached to the stage 200 via pins, screws etc. Shielding 224 isprovided with a passageway 226 e.g. in a cone shape that extends fromand aligns with the passageway 222 in the primary collimator 208. Acircular channel 228 is provided on the bottom side of the shielding 224to provide a travel path or clearance for photon flattening filters 302to rotate about an axis as will be described in more detail below. Acentral opening 230 in the shielding 224 allows a structural member 306passing through to fixedly attach the filter-foil assembly 300 to thestage 200 (see also FIG. 1C).

The stage 200 may be configured to support an axis such as a rotationaxis 312, which is adapted to rotate or move the filter-foil assembly300 as will be described in more detail below. For example, the stage200 may have a U-shaped cutout at a side to provide space for therotation axis 312. The rotation axis 312 may be supported by a bracket,which may be attached to the stage 200 by e.g. screws.

FIG. 3 is a perspective view of a filter-foil assembly or beam filterassembly 300 in accordance with some embodiments of the invention. Forclarity photon flattening filters are not installed or shown in FIG. 3.The filter-foil assembly 300 supports one or more beam filters. Forexample, the filter-foil assembly 300 may support photon flatteningfilters 302 and electron scattering foils 304, and positions the two inphoton modes and in electron modes respectively (see also FIG. 1C). Thefilter-foil assembly 300 is operable to move in a linear direction androtate around an axis. Alternatively, the filter-foil assembly isoperable to translate in both X- and Y-directions. The linear movementof the filter-foil assembly 300 can be accomplished by moving the stage200 which is driven by the axis 212. The filter-foil assembly 300 can befixedly attached to the stage 200 via a structural member 306 using e.g.pins, screws or other suitable means 308. The structural member 306 iscoupled to the filter-foil assembly 300 via a bearing assembly 310including bearing rings, bearing retainer, bearings etc. The bearingassembly 310 allows the filter-foil assembly 300 to rotate with respectto the structural member 306. The rotation of the filter-foil assembly300 can be actuated and controlled by the rotation axis 312, which issupported by the stage 200. The rotation axis 312 includes a motor 312a, a pulley 312 b, roller guides 312 c, and a timing belt 312 d (seealso FIGS. 2, 1C, and 1D). The timing belt 312 d (FIG. 1D) is woundaround the pulley 312 b and the filter-foil assembly plate 316 b.Therefore, when actuated, the motor 312 a drives the pulley 312 b toturn, which transmits the rotation force to the timing belt 312 d. Thetiming belt 312 d engages filter-foil assembly plate 316 b and rotatesit around the structural 306. The roller guides 312 c can be adjusted tocontrol the driving force transmitted to the filter-foil assembly 300. Aresolver or sensor 314 can be coupled to the motor 312 a to provideprimary control feedback. A second housed resolver may be used toprovide redundant or secondary feedback. Preferably, the motor 312 a isa servo motor electrically connected to a controller and is operablewith user interface software. It should be appreciated that while aspecific motor, roller guides, and feedbacks are described in detail forillustrative purposes, other types of drive mechanisms or feedbackdevices can also be used and anticipated by the inventors. The beamfilter assembly can be driven by either a linear axis or a rotationaxis, or both, or by two linear axes in X-Y directions to position abeam filter or adjust the position of a beam filter.

As illustrated in FIG. 3, the filter-foil assembly 300 includes asupporting structure 316 such as a plate or the like configured tosupport or position one or more beam filters such as a plurality ofphoton flattening filters 302 and electron scattering foils 304. Forclarity photon flattening filters 302 are not shown in FIG. 3. In somepreferred embodiments, the photon flattening filters 302 are positionedin a circular or partial circular configuration having a first radius.The scattering foils 304 are positioned in a circular or partialcircular configuration having a second radius. The second radius ispreferably different from the first radius. For example, the electronscattering foils 304 may be positioned in a partial circularconfiguration at locations proximate to the periphery of the plate 316,and the photon flattening filters 302 may be positioned in a circular orpartial circular configuration at locations proximate to the midpoint ofthe radius of the plate 316.

In some preferred embodiments, the plate 316 may include a first portion316 a supporting electron scattering foils 304 or other elements, and asecond portion 316 b supporting photon flattening filters 302. The firstand/or second portions 316 a, 316 b may be in a circular shape or otherregular or irregular shapes. The second portion 316 b may be attached tothe first portion 316 a by e.g. screws or other suitable means. Thesecond portion 316 b may have a plurality of ports 318 configured toreceive a plurality of beam filters such as photon flattening filters302. In FIG. 3, six ports are shown in the second portion 316 b. Itshould be noted that a different number of ports can be provided. Thephoton flattening filters 302 can be in various forms including e.g.conical form, and can be held in the ports 318 by pins, screws or othersuitable means. The conical filters 302 may point upwards or downwardsfrom the plate 316. The materials, forms and/or configuration of thephoton flattening filters 302 can be chosen to match the energy of theX-rays produced based on specific applications.

The electron scattering foils 304 may include primary scattering foils304 a and secondary scattering foils 304 b. The combination of primaryand secondary scattering foils 304 a, 304 b may provide a broadened,uniform profile of a treatment beam. Nine pairs of electron scatteringfoils are shown in FIG. 3, six grouped together on one side and threegrouped together on the opposite side. It will be appreciated that adifferent number of electron scattering foils can be provided. Theprimary foils 304 a may be supported by a bridge structure 320 mountedto the first plate portion 316 a. The bridge structure 320 may raise theprimary foils 304 a above the secondary foils 304 b and verticallyaligns a primary foil with a secondary foil. The increased distancebetween the primary and secondary scattering foils allows the primaryscattering foils to be higher in the treatment head and closer to thesame elevation or location where the photon source (the target) islocated. Having the source of electrons and the source of photons at anabout same location is desirable since treatment planning and otherdesign aspects of the treatment head are generally optimized around thelocation of the photon source. The increased separation between theprimary and secondary electron foils also makes electron beamperformance less sensitive to small machining variations in thethickness of the secondary foils and in the separation distance. Anelectron foil assembly with small separation between the upper and lowerfoils requires tighter tolerances on spacing and thickness of the lowerfoils to achieve uniform electron beam performance.

The linear axis 212 and rotation axis 312 or two linear axes allow forautomated adjustments of the position of the electron scattering foils304 and photon flattening filters 302. The motorized axes 212, 312 maybe controlled by a computer and adjustments can be made using a softwareinterface rather than manual adjustment as in the prior art. With asuitable 2D radiation sensor (such as a grid ion chamber array) and anautomated tuning software application, these adjustments can be madewithout human intervention.

The use of both rotation and linear axes 212, 312 to adjust the positionof electron scattering foils and photon flattening filters makes itpractical to place the foils 304 and filters 302 on a different radiusof a carousel assembly 300. To position the filters and foils at twodifferent radii allows for a greater number of filters or foilsavailable at two radii, as compared to confining both the filters andfoils at a same radius. A greater selection of filters and foils mayallow for a greater selection of X-ray and electron energies.

The two-radius design of filter-foil assembly 300 makes it possible thatthe primary collimator 208, a large piece of radiation shielding locatedaround the photon flattening filters 302, to be absent when usingelectron scattering foils 304 in electron modes. The absence of theprimary collimator 208 improves the performance in electron modes byreducing scatter.

The two-radius design also allows for a smaller inner radius for theflattening filters 302. A smaller inner radius of the filter travel path228 would introduce a greater curvature in the shielding 224 gaps, hencesubstantially reducing the direct radiation leakage paths which wouldotherwise require heavy and expensive shielding plugs.

The use of a separate inner radius for filter motion allows for a large,simple and effective primary collimator 208. Prior art designs havesignificant compromises to the primary collimator below the target. Inmost prior designs, the primary collimator is fixed and chopped up incomplex and inefficient ways to allow motorized filters and foils topenetrate it. Earlier designs place primary collimator shielding furtherfrom the radiation target requiring significantly greater mass,complexity and cost of shielding components.

Returning to FIG. 3, in some preferred embodiments, a mirror 420 can beinstalled on the filter-foil assembly 300. The mirror 420 constitutes amember of a field light assembly 450 and serves to reflect light from alight source. Because the mirror 420 is located on the filter-foilassembly 300, it can be moved out of the way of the radiation orelectron beam by motorized axes 212 and 312 when it is not used in fieldlight simulation. As a result, the mirror 420 is not required to betransparent to electron or radiation beams and can be made from anysuitable materials, including a thin film or preferably a more robustmaterial such as metal, glass etc. This is advantageous over prior artmirrors which are typically made of a thin film transparent to radiationor electron beams since it is fixedly located in the beam centerline.Thin film materials such as Mylar are more susceptible to degradationdue to exposure to radiation, damage and optical distortion. They mayalso cause scattering losses and beam contamination.

Another benefit of disposing the field light mirror on the carouselassembly or beam filter positioning device is that the radiationshielding in the collimator assembly can be greatly simplified. In priorart accelerators, the field light mirror is typically located in thecollimator assembly above the jaws, necessitating complex shieldingdesign to allow for mounting and service of the mirror. The accessallowances require shielding voids that are duplicated for symmetry,resulting in inefficient shielding requiring complicated, expensivemilled pieces of shielding such as tungsten to meet shieldingrequirements. Without a mirror in the collimator assembly, symmetricalshape of less expensive shielding such as molded lead can be used. Thiswould result in an improvement in electron scatter due to the moreefficient shielding.

FIG. 4 is a perspective view of an exemplary ion chamber assembly 400 inaccordance with some embodiments of the invention. The ion chamberassembly 400 is located under the filter-foil assembly 300 for detectingthe parameters of a treatment beam such as beam energy, dosedistribution, and dose rate etc. The ion chamber 402 can be supported bya structural member 404 such as a bracket, which is attached to amovable member such as a plate 406. The plate 406 is driven by an axissuch as a linear axis 408 which is supported by a support member such asa plate 410. The support plate 410 is attached to the base plate 202 andthe frame 204. The linear axis 408 includes a motor 408 a, a ball screw408 b, a coupler 408 c coupling the motor and the ball screw, and a ballnut 408 d engaging the ball screw. The motor 408 a can be supported by amount 412, which is attached to the support plate 410. The ball nut 408d is fixed to or otherwise engaged with the plate 406. The motor 408 aserves to rotate the ball screw 408 b through the coupler 408 c. Theball nut 408 d is engaged with the ball screw 408 b and moves linearlyas the ball screw 408 b rotates. The plate 406 to which the ball nut 408d is fixed moves linearly as the ball nut 408 d moves. Linear guiderails 412 a, 412 b fixedly attached to the support plate 410 define thelinear movement of the plate 406. Slide guides (not shown) or othersuitable mechanisms can be used to engage the plate 406 with the guiderails 412 a, 412 b. Therefore, when actuated, the motor 408 a rotatesthe ball screw 408 b, and moves the ball nut 408 d and the plate 406 ina linear direction. The ion chamber 402, which is supported by thebracket 404 attached to the plate 406, moves with the plate 406 alongthe guide rails 412 a, 412 b in a linear direction. A cable duct 414(see also FIG. 1B) is attached to the bracket 404 to house variouscables connected to the ion chamber 402. A resolver or sensor 408 e canbe coupled to the motor 408 a to provide primary feedback on theposition of the ball screw 408 b. A second housed resolver 408 f may beused to provide redundant or secondary feedback. A rack and pinion gearassembly 413 may be used to provide additional feedback. Preferably, themotor 408 a is a servo motor electrically connected to a controller andis operable with user interface software. It should be appreciated thatwhile a specific motor, ball screw, and feedbacks are described indetail for illustrative purposes, other types of drive mechanisms orfeedbacks can also be used and anticipated by the inventors. It shouldbe noted that the ion chamber can be driven, positioned, or adjusted byeither a linear axis or a rotation axis.

The bracket 404 may include an extension member 416. Two light sourcessuch as filament lamps 418 a, 418 b can be mounted proximate to the endof the extension member 416. The light sources 418 a, 418 b, togetherwith the mirror member 420 installed on the filter-foil assembly 300,forms a field light assembly 450. The extension member 416 distances theion chamber 402 from the light sources 418 a, 418 b.

In a photon mode operation, the ion chamber 402 is located under aphoton flattening filter 302 for detection of the parameters of atreatment beam. In an electron mode operation, the ion chamber 402 islocated under an electron scattering foil in the beam centerline fordetection of the parameters of a treatment beam. In field lightsimulation, the linear axis 408, rotation axis 312, and linear axis 212work collectively to adjust the position of the light source 418 a or418 b and mirror 420 to optically project the light source to a virtualposition coincident with the same location of the radiation source. Thethree degree of freedom (X, Y, and Z) adjustment of the virtual lightsource can be accomplished by mounting the mirrors and light sources onmotion axes already needed for other purposes. No additional motion axesneed to be provided to achieve the three degree of freedom adjustment.

The use of motorized axes to move the lamp and mirror assemblies allowsfor automated adjustment of the field light system. The motorized axescan be controlled by a computer and the adjustment of the field lightsystem can be performed using a software interface rather than theexisting manual process. This would save factory adjustment time.

Because the lamp assembly 418 is mounted to a motorized axis 408,additional spare lamps can be added to the motorized axis 408 and movedinto place in the event that a lamp fails. Both lamps may be factoryadjusted into position relative to the assembly interface. Automaticallyswitching to a spare lamp in the event that a light bulb fails allows amedical linear accelerator to continue to be used for treating patientsuntil the failed lamp is replaced at a convenient time.

Referring to FIG. 1B, the beam filter positioning device 100 may furtherinclude a backscatter filter 460 located under the ion chamber assembly400. A backscatter filter 460 such as a thin tantalum filter passes highenergy photons in the beam direction, but stops low energy photonsprimarily caused by upward scatter off the upper collimator jaws locateddownstream. The backscatter filter 460 can greatly reduces unwantedbackscattered radiation into the ion chamber 400. This scatteredradiation has an unwanted effect on the calibration of the ion chamber402.

The backscatter filter 460 can be supported by a structure 462, whichcan be fixedly attached to the bottom portion of the structural member306 e.g. with screws. The backscatter filter 460 can therefore be movedtogether with the filter-foil assembly 300 in a direction. Preferablythe backscatter filter 460 is positioned to have a radius from thestructural member 306 about the same as for the photon flatteningfilters 302, so that when in an electron mode, the backscatter filter460, like the photon flattening filters 302, can be moved out of thepath of an electron beam. Preferably, the structure 462 is a box-likestructure having an upper plate and a lower plate with the backscatterfilter 460 being attached to the lower plate. The box-like structure 462is preferably side open to allow the ion chamber 402 passing though thestructure 462 between the upper and lower plates. In some embodiments,the backscatter filter 460 can be moved by a rotation axis.

FIG. 5 is a perspective view of an exemplary target assembly 500 inaccordance with some embodiments of the invention. The target assembly500 positions a target in the beam path for generation of X-rays in aphoton mode, or moves a target out of the beam path in an electron mode.The target assembly 500 can be fixedly attached to the base plate 202via a channel mount 502. The target assembly 500 includes a substrate504 supporting one or more target buttons 506 and a cooling tube 508coupled to the substrate 504 for supplying a cooling fluid. Channels canbe provided in the substrate 504 adjacent or surrounding the targetbuttons 506 for circulating a cooling fluid to dissipate heat generatedduring target operation. The substrate 504 and the cooling tube 508 canbe supported by a mount assembly 510, which is movable relative to thechannel mount 502. A shielding block 512 is placed atop and attached tothe mount assembly 510 by e.g. screws or pins.

The target assembly 500 can be moved by a linear axis 514. The linearaxis 514 includes a motor 514 a, a ball screw (not shown), a coupler 514b coupling the motor and the ball screw, and a ball nut 514 c engagingthe ball screw. The motor 514 a can be supported by mount 516, which isattached to the channel mount 502. The ball nut 514 c is fixed to orotherwise engaged with shielding block 512. The motor 514 a serves torotate the ball screw through the coupler 514 b. The ball nut 514 c isengaged with the ball screw and moves linearly as the ball screwrotates. As a result, the shielding block 512, to which the ball nut 514c is fixed, moves linearly as the ball nut moves. The mount assembly510, which supports the substrate 504 and cooling tube 508 and isattached to the shielding block 512, moves linearly as the ball nut 514c moves. Linear guide rail (not shown) fixedly attached to the channelmount 502 defines the linear movement of the mount assembly 510. Slideguides (not shown) can be used to engage the mount assembly 510 with theguide rail. A resolver or sensor can be coupled to the motor 514 a toprovide primary feedback on the position of the ball screw. A secondhoused resolver may be used to provide redundant or secondary feedback.Preferably, the motor 514 a is servo motor electrically connected to acontroller and is operable with user interface software. It should beappreciated that while a specific motor, ball screw, and feedbacks aredescribed in detail for illustrative purposes, other types of drivemechanisms or feedbacks can also be used and anticipated by theinventors. It should also be noted that the target assembly can bedriven, positioned, or adjusted by either linear axis or a rotationaxis.

The target assembly 500 may include one or more targets each beingoptimized to match the energy of an incident electron beam. For example,the target assembly 500 may include a first target 506 a adapted for afirst photon mode, a second target 506 b for a second photon mode, and athird target 506 c for a third photon mode. The material of a target canbe chosen and/or the thickness of a target be optimized for an incidentelectron beam with a particular energy level. By way of example, a firsttarget 506 a may be optimized for an incident electron beam having anenergy level ranging from 4 to 6 MV. A second target 506 b may beoptimized for an incident electron beam having an energy level rangingfrom 8 to 10 MV. A third target 506 c may be optimized for an incidentelectron beam having an energy level ranging from 15 to 20 MV. It shouldbe noted that a different number of targets may be included in thetarget assembly 500. In operation, the linear axis 514 moves orpositions one of the targets 506 in the beam path for a photon mode. Inan electron mode, the linear axis 514 removes the targets 506 out of thebeam path to allow an electron beam passes unimpeded.

FIG. 6 illustrates an exemplary beam filter positioning device orcarousel assembly 100 in a photon mode operation in accordance with someembodiments of the invention. The primary collimator 208 and shielding224 have been positioned and aligned in the beam centerline. The ionchamber 402 and the backscatter filter 460 have also been positioned inthe beam centerline. Rotation axis 312 is actuated to rotate thefilter-foil assembly 300 clockwise or counter-clockwise to align one ofthe photon flattening filters 302 in the beam centerline. Sequentiallyor simultaneously, the linear axis 514 is actuated to position a targetbutton 506 in the beam centerline. An electron beam 602 impinges thetarget button 506 and X-rays 604 are produced. The field of X-rays 604is shaped as the X-rays produced pass through the passageways in theprimary collimator 208 and shielding 224. A radiation beam with auniform dose distribution is obtained as the X-rays pass through aflattening filter 302. The parameters of the treatment beam are detectedas the beam passes through the ion chamber 402. Backscatter filter 460located under the ion chamber 402 blocks backscatter radiation fromentering the ion chamber 402 to ensure accurate measurement of theradiation beam parameters. Because the mirror 420 is installed on thefilter-foil assembly 300 and is off the beam centerline in the photonmode, the treatment beam generated pass downstream unimpeded by themirror. Depending on the energy of an incident electron beam 602 for aparticular application, the linear axis 514 may move the target assembly500 to position a target button 506 this is optimized for such beamenergy in the beam path for optimized performance of the target.Similarly, depending on the energy of an incident electron beam, therotation axis 312 may rotate to position a flattening filter 302 that isoptimized for such beam energy in the beam centerline for optimizedperformance of the filter.

FIG. 7 illustrates an exemplary beam filter positioning device orcarousel assembly 100 in an electron mode in accordance with someembodiments of the invention. In an electron mode, linear axis 514 isactuated and drives the target assembly 500 to move the target 506 awayfrom the beam centerline. Linear axis 214 is actuated and drives thestage 200 to move the primary collimator 208, shielding 224, andbackscatter filter 460 away from the beam centerline. Because theelectron scattering foils 304 have a different or greater radius thanthe photon flattening filters 302 on the filter-foil assembly 300,driving the filter-foil assembly 300 to move the flattening filters 302away from the beam centerline would bring the scattering foils 304 tothe beam centerline. Rotation axis 312 is actuated and the filter-foilassembly 300 rotates clockwise or counterclockwise to align one of theelectron scattering foils 304 with beam centerline. The primary andsecondary scattering foils 304 scatter the electron beam to produce abroadened, uniform profile of a treatment beam 606. Depending on theenergy of an incident electron beam for a particular application, therotation axis 312 may rotate the filter-foil assembly 300 to align ascattering foil that is optimized for such beam energy in the beam pathfor optimized performance of the foil. The parameters of the treatmentbeam are detected as the beam passes through the ion chamber 402.

FIG. 8 illustrates an exemplary beam filter positioning device orcarousel assembly in a field light simulation mode in accordance withsome embodiments of the invention. Linear axis 408 is actuated anddrives the ion chamber assembly 400 to move the ion chamber 402 awayfrom the beam centerline. Linear axis 214 is actuated and drives thestage 200 to move the primary collimator 208, shielding 224, andbackscatter filter 460 away from the beam centerline. Because the mirrormember 420 has a greater radius than the photon flattening filters 302on the filter-foil assembly 300, driving the filter-foil assembly 300 tomove the flattening filters 302 away from the beam centerline wouldbring the mirror member 420 to the beam centerline. Rotation axis 312 isactuated and rotates the filter-foil assembly 300 clockwise orcounterclockwise to position the mirror member 420 in the beamcenterline. The linear axis 408 moves and adjusts the position of a lamp418 to project the lamp filament to a virtual radiation source position802. Mirror 420 reflects light projected from the lamp 418 to illuminatean area e.g. on the surface of a patient's skin for simulation.

One of the advantages of the beam filter positioning device of theinvention is that it can be configured to automatically adjust theposition of beam filters, field light assembly, or other devicecomponents. The automatic adjustment can be accomplished by a controlsystem operable by a computer software interface such as a GraphicalUser Interface (GUI). The control system may include a processor such asfor example, a digital signal processor (DSL), a central processing unit(CPU), or a microprocessor (μP), and a memory coupled to the processor.The memory serves to store programs for the operation of the beam filterpositioning device and other programs. The processor executes theprogram and generates signals for operation of the motion axes or othercomponents of the beam filter positioning device. Responsive to thesignals from the control system, the beam filter positioning deviceoperates in which one or more motion axes move the beam filters, fieldlight source, mirror, or other device components in a controlled andautomatic manner based on a plan or routine, or based on a demand inputfrom a user. The control system also receives feedback signals fromsensors or resolvers in the motion axes, or from other device componentssuch as the ion chamber, and generates signals for adjustment whennecessary. For example, based on the beam parameter signals provided bythe ion chamber to the control system, the control system mayrecalculate and generate signals for adjustment to the motion axes. Themotion axes respond and automatically adjust the position of the beamfilters. Similarly, based on the field light image or information, thecontrol system may recalculate and generate signals for adjustment tothe motion axes. The motion axes respond and automatically adjust theposition of the light source and/or mirror to adjust the virtual lightsource position in three degrees of freedom.

Exemplary embodiments of beam filter positioning devices or carouselassemblies have been described. Those skilled in the art will appreciatethat various modifications may be made within the spirit and scope ofthe invention. All these or other variations and modifications arecontemplated by the inventors and within the scope of the invention.

What is claimed is:
 1. A modular assembly comprising: a base member; astage member movable relative to the base member; a filter-foil devicecoupled to and thereby moveable with the stage member, said filter-foildevice comprising a body, one or more photon flattening filters and oneor more electron scattering foils supported by the body, the body beingmovable relative to the stage member in positioning the photonflattening filters or electron scattering foils; and a target devicesupported by the base member, said target device comprising a substrateand one or more targets supported by the substrate, the substrate beingmovable in positioning the one or more targets.
 2. The modular assemblyof claim 1 which comprises: a first driving device supported by the basemember, the first driving device being operable to move the stage memberand the filter-foil device coupled to the stage member relative to thebase member; a second driving device supported by the stage member, thesecond driving device being operable to move the body of the filter-foildevice; and a third driving device supported by the base member, thethird driving device being operable to move the substrate supporting theone or more targets of the target device.
 3. The modular assembly ofclaim 2 which further comprises: an ion chamber device; and a fourthdriving device supported by the base member, the fourth driving devicebeing operable to move the ion chamber device relative to the basemember.
 4. The modular assembly of claim 3 which further comprises afield light device, the field light device comprising a mirror membersupported by and thereby being movable with the body of the filter-foildevice, and one or more light sources supported by and thereby movablewith the ion chamber device.
 5. The modular assembly of claim 3 whereinat least one of the first, second, third, and fourth driving devicescomprises a servo motor and one or more feedback devices.
 6. The modularassembly of claim 3 wherein each of the first, second, third, and fourthdriving devices comprises a servo motor and one or more feedbackdevices.
 7. The modular assembly of claim 1 wherein the one or morephoton flattening filters are arranged in an arc or a circularconfiguration having a first radius, and the one or more electronscattering foils are arranged in an arc or a circular configurationhaving a second radius that is different from the first radius.
 8. Themodular assembly of claim 1 wherein the stage member is movable relativeto the base member in a linear direction, and the body of thefilter-foil device is movable at least in a rotary direction.
 9. Asystem comprising a beam filter positioning device and a controlleroperable to control the beam filter positioning device using a computersoftware embodied in a non-transitory computer readable medium, whereinthe beam filter positioning device comprises: a base member; a stagemember movable relative to the base member; a filter-foil device coupledto and thereby moveable with the stage member, said filter-foil devicecomprising a body, one or more photon flattening filters and one or moreelectron scattering foils supported by the body; a first driving devicesupported by the base member and being operable to move the stage memberand thereby the filter-foil device coupled to the stage member relativeto the base member; and a second driving device supported by the stagemember and being operable to move the body of the filter-foil device andthereby the photon flattening filters and electron scattering foilssupported by the body relative to the stage member; and wherein thefirst and the second driving devices are controllable by the controllerusing the computer software.
 10. The system of claim 9 wherein each ofthe first and second driving devices comprises a servo motor and one ormore feedback devices which are coupled to the controller, and thecontroller is operable to control the servo motor based on at leastsignals from the one or more feedback devices.
 11. The system of claim10 wherein the beam-filter positioning device further comprises: atarget device supported by the base member, the target device comprisinga substrate and one or more targets supported by the substrate; and athird driving device supported by the base member and operable to movethe substrate and thereby the one or more targets supported by thesubstrate; wherein the third driving device comprises a servo motor andone or more feedback devices which are coupled to the controller, andthe controller is operable to control the servo motor of the thirddriving device based on at least signals from the one or more feedbackdevices of the third driving device.
 12. The system of claim 11 whereinthe beam-filter positioning device further comprises: an ion chamberdevice; and a fourth driving device supported by the base member, thefourth driving device being operable to move the ion chamber devicerelative to the base member; wherein the fourth driving device comprisesa servo motor and one or more feedback devices which are coupled to thecontroller, and the controller is operable to control the motor of thefourth driving device based on at least signals from the one or morefeedback devices of the fourth driving device.
 13. The system of claim12 which further comprises a field light device, the field light devicecomprising a mirror member supported by and thereby being movable withthe body of the filter-foil device, and one or more light sourcessupported by and thereby movable with the ion chamber device.
 14. Thesystem of claim 12 wherein the controller is operable to control: thefirst driving device to move the stage member in a linear direction; thesecond driving device to move the body of the filter-foil device in arotary direction; the third driving device to move the substrate in alinear direction; and the fourth driving device to move the ion chamberdevice in a linear direction.
 15. The system of claim 9 wherein the oneor more photon flattening filters are arranged in an arc or a circularconfiguration having a first radius, and the one or more electronscattering foils are arranged in an arc or a circular configurationhaving a second radius that is different from the first radius.
 16. Thesystem of claim 9 wherein the controller is operable to control: thefirst driving device to move the stage member in a linear direction; thesecond driving device to move the body of the filter-foil device in arotary direction.